The present invention relates to a motor vehicle headlamp which is provided with a leveling gauge for determining whether or not the angle of irradiation of the light beam emitted by the headlamp is properly oriented in upward and downward directions, and more particularly to such a motor vehicle headlamp which permits easy adjustment of the angle of irradiation of the headlamp beam.
A headlamp is generally provided with an aiming mechanism capable of adjusting the irradiating direction of the headlamp in both horizontal and vertical directions so as to adjust the angle of irradiation of the headlamp beam within a prescribed range. (This adjustment is hereinafter referred to as an "aiming adjustment"). To perform an aiming adjustment, the headlamp is turned on in a dark room with the beam of the headlamp being directed onto a screen at a prescribed distance from the headlamp, and the aiming mechanism is then adjusted so that the irradiated spot on the screen is set at a prescribed position.
However, the conventional aiming adjustment described above requires costly facilities and instruments such as a large dark room and a screen. Furthermore, the conventional aiming adjustment presents a problem in that it takes a significant amount time to complete the adjusting work since is necessary to perform the aiming adjustment through observation of the screen.
Headlamps approved for use in the United States generally have three location bosses provided in the form of protrusions on the lens in the front part of the unit. A measuring instrument called an "aimer" is set in direct contact with the location bosses to determine whether or not the beam of the headlamp is properly adjusted in relation to the horizontal plane. For this purpose, the front end surfaces of the location bosses are shaped and disposed so as to define a vertical plane when the motor vehicle is in a level state. The amount of inclination of the headlamp in relation to the horizontal plane can be measured with the aimer set in such a way as to use the front end areas of these location bosses with which it is in direct contact as a datum plane.
It is required that the measured value (the measured amount of inclination) as determined with the aimer be within a prescribed range. Accordingly, it is absolutely necessary to provide these location bosses on headlamps for use in the United States. This requirement has proved troublesome in that headlamps for use in the United States must be manufactured separately from those for use in Japan or Europe.